Surprise medical bills have gotten more common and more expensive, according to a new study published in the Journal of the American Medical Association.

These bills can be devastating to patients, even those who have some savings and a steady source of income.

The big picture: The study used an Optum database to look at patients covered by a large commercial insurer who received either inpatient or emergency care at hospitals covered by their insurance, and got a bill for out-of-network care.

These bills were probably unexpected. Patients often assume that the care they receive at an in-network hospital will all be covered by their insurer.

The Trump administration's newly finalized “public charge” rule extends a series of policy changes that could negatively affect the health of both legal and undocumented immigrants in the U.S., Dave Chokshi of NYC Health + Hospitals writes for Axios Expert Voices.

The rules make the use of certain public assistance programs grounds for denying immigrants lawful permanent residence.

An Urban Institute study showed that, in 2018, 1 in 5 adults in low-income immigrant families did not participate in a government benefit program like Medicaid for fear of risking future green card status.

What to watch: The Homeland Security Department's “public charge” rule is likely to be challenged in court before Oct. 15, when it's scheduled to take effect.

Chokshi is the chief population health officer at New York City Health + Hospitals and a primary care physician at Bellevue Hospital.

3. Wealthier people ditch ACA exchanges

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Data: Centers for Medicare & Medicaid Services; Chart: Axios Visuals

The universe of people covered by the Affordable Care Act keeps narrowing, Axios' Sam Baker reports.

Between the lines: People who make too much money to qualify for help paying their premiums are fleeing the ACA’s insurance exchanges. But the exchanges are still pretty stable for people who receive premium subsidies, according to new federal data.

You can see two clear trends in these data.

First, unsubsidized enrollment has fallen as premiums continue to rise. That makes sense: If you’re on the hook for your entire premium, you’re more likely to bail when those premiums rise.

Overall enrollment tapered off under the Trump administration, which also makes sense: Trump’s policy decisions contributed to big premium spikes in 2018, and he has also expanded access to non-ACA options that may be more attractive to healthier, unsubsidized people.

Sam's thought bubble: This is the continuation of a somewhat ironic trend. As the ACA’s coverage expansion has shrunk, the law has evolved to look more like a traditionally liberal health care program.

Part of the initial goal was to create a competitive marketplace that would benefit even the middle class households too wealthy for a premium subsidy.

That’s the part that has fallen by the wayside as the ACA’s coverage expansion has narrowed down. Now it’s mainly direct government assistance — through Medicaid and premium subsidies — that’s concentrated among the poorest households.

Public health officials announced Monday they had gathered enough preliminary data to determine that 2 of the 4 investigational treatments for Ebola performed better than the others, my colleague Eileen Drage O'Reilly reports.

A trial in the Democratic Republic of Congo has been dropped to focus on a new extension trial for the 2 monoclonal antibodies.

Why it matters: There are no FDA-approved treatments for Ebola. Researchers testing drugs during the DRC's largest outbreak found a cocktail of 3 antibodies called REGN-EB3 was most effective, followed closely by monoclonal antibody 114.